Amine curing agents for single component epoxy resin adhesives for plastics are well known in the art, as taught by West in U.S. Pat. No. 2,828,236. Lehmann et. al., in U.S. Pat. No. 3,860,541, in order to improve curing times for epoxy adhesives, developed a composition containing a solid epoxy resin, and a solid curing agent consisting of the cooled admixture of an adduct of an epoxy resin with an aromatic or cycloaliphatic amine reacted at 80.degree. C. to 200.degree. C., and a liquid polyamine. The solid epoxy resin and the solid adduct-polyamine curing agent are mixed together to form an adhesive powder. This adhesive powder may be sprinkled on various fabrics or plastic sheets and hot rolled at about 80.degree. C. to 130.degree. C. to provide a cured adhesive film.
Cams et. al., in U.S. Pat. No. 2,786,794, taught hot melt adhesives for metals. Metal adhesion presents special problems due to the low porosity of most metal surfaces. Cams et. al. solved this problem by providing a solventless composition comprising an unreacted mixture of an epoxy resin and up to about 10 wt.% of a dicyandiamide or melamine and/or a polyamine such as ethylene-diamine, N:N-diethylene diamine or triethylene-tetramine as a hardening agent.
This unreacted composition can be formed into cold compressed solder sticks, which melt upon contact with hot metal surfaces, to form a very thin fluid which fills low porosity metal and glass surfaces. The composition can also be brushed onto the surfaces in molten, paste, or solution form. Hardening in Cams et. al., is conducted by heating at between 100.degree. C. to 200.degree. C., while the surfaces are pressed together by a vise, clamp, or other pressing equipment which goes through the curing cycle with the metal and adhesive. Shear strengths of about 1,450 psi. are acheived.
What is needed, is an adhesive composition that can be brushed onto joint surfaces or formed into intricate shapes to match joint geometry, has a long shelf life, allows at least 1/2 minute working time after melt bonding, cures at low temperatures, and which will provide joint shear strengths of at least about 1,000 psi. without requiring the extensive use of pressing equipment. The elimination of clamps in the curing process would be particularly advantageous in any continuous, commercial, production line operation requiring metal to metal bonding.